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    <title>Document</title>
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    <script>
        var arr = [2, 1, 2, 1, 4]
        // 思路一：
        // console.log([...new Set(arr)]);
        // 思路二
        // var arr1 = []
        // arr.forEach(item => {
        //     if (!arr1.includes(item)) {
        //         arr1.push(item)
        //     }
        // })
        // console.log(arr1);
    </script>
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